Fuse



Oct. 28, 1930. N, J, CONRAD y 1,779,929

FUSE

Filed Jan'. 28, 1927 2 Sheets-Sheet 2 @4' S@ @a 5,6, as @687 7345,@

Patented Oct. 1930 UNITED STATES PATENT ori-TCE NICHOLAS J. CONRAD, F WIIJIETTE, ILLINOIS, ASSIGNOB, BY MESNE ASSIGNMENTS,

T0 SCHWEITZEB @c CONRAD, INC., OF CHICAGO, ILLINOIS, A CORPCRATION 0F DELA- WARE FUSE

Application mea 'January as, 1927. serial No. 164,155.

This invention relates to electric fuses, and more particularly, to that type of fuse in which a movable terminal element is drawn through a suitable liquid for quenching the arc. In known fuse structures ot this general type which are now on the market as the Schweitzer and Conrad fuses, the fuse proper is formed preferably 4ot a metal or alloy, which is mechanically weak, necessitating 1o means other than the fuse for restraining the movable terminal member and holding it in normal operative position. While this general type of fuse structure has proved to be highly satisfactory, for currents of appreciable value, I have found that particularly in small capacities it can be improved upon by providing in connection with a ine conductor of very small cross sectional area, suitable mechanical means for connecting the fuse to the movable terminal member in such man ner as.to give the fuse a mechanical advantage over the operating means tending tomove the movable terminal away from the ferrule or ixed terminal. It is, therefore, one

of the mainobjects of my invention to provide simple and eilicient means whereby a use of very small cross sectional areamay be employed for normally maintaining the movable terminal member in operative relation to the fixed terminal member or ferrule, such means being so constructed and arranged that the major portion of the force exerted by the springor equivalent means for operating the movable terminal member is taken by such connection, a small portion onl of the tension of lthe spring being exerted, on the fuse so as to maintain it under stress. In its broader aspect, the present invention involves the broad idea of an electrical connection or fuse operating at a mechanical advantage betweenthe movable contact or terminal member, this connection being maintained l normally operative by the mechanical ilitegrity of the electrical connectionor` fuse and rendered inoperative upon destruction or failure'of said connection or fuse sov as to release the movable terminal member.'

' A further improvement here involved resides in the interchangeability of the present fuse connection with previously used. fuse line 4-4 of Fig.

Fig. 5 is a section taken substantially on line 5--5 of Fig. 3; Y

Fig. 6 is a section taken substantially on line 6-6 of Fig. 3;

Fig. 7 is a detail, partly in section, of a modified form of terminal member securing means: and

Fig. 8 is a detail, partly in section, of a second modified form of terminal member securing means.

- The general construction of the device as a whole is disclosed'in detail in my co-pending application for use device and the like, filed Aprill 11, 1923, Serial No. 631,263, and need not be discussed in detail in the present case. The fuse structure includes a barrel l of glass the ends of which t into upper and lower ferrules 2 and 3, respectively, the errules being secured in position by a suitable alloy iilling 4 which also serves as a packing for producing a iuid tight closure. A flanged vblow-out disc 5 is secured in the upper end or top of the upper errule by means of a non-'hardening cement, this disc being under severe conditions blown out by the gases resulting from blowing of the fuse.

A. movable terminal member 6 is secured to the upper end of a tension spring 7 within ,barrel vl by means of pins 8 passing between the upper convolutions of the spring, these pins being secured in a collar 9 which Vtits about member 6 and is'secured thereto by a screw 10 threaded through the collar and projecting into a suitable bore 11 in the terminal member. Member 6 is provided at its lower end with a depending sleeve 12 into which is inserted the upper portion of a flexible braided conductor 13, the sleeve being deformed upon the conductor so as to securely clamp the same. The lower end of the conductor 13 is similarly secured in a sleeve 14 secured to ferrule 3, andthe lower end of spring 7 is also secured to this ferrule. The conductor 13 carries the greater portion of the current Howing through the fuse structure and prevents undue heating of spring 7 with possible impairment of the strength or resillency ofthe s rm PA ligquid director 15 in the nature of a relatively wide and thick collar is supportedin spaced relation about member 6 concentric therewith by means of a suitable number of supporting pins 16 which are rounded at their ends, the outer ends of these pins fitting into a corresponding groove in the inner face of director 15 and the inner ends of the pins proan upwardly converging hollow or frusto-v conical shaped opening or nozzle 19 for ejecting the quenching liquid upon downward movement of the terminal member 6. This serves to project a Stream or current of the liquid upwardly and is of material assistance in quenching the arc.

The present invention relates more partie ularly to the fuse proper and the means for connecting this fuse to the terminal member 6 1n such manner as to give the fuse a mechanical advantage over the spring 7 enabling the fuse to maintain the connection mechanically while insuring a quick break upon melting of the fuse. A supporting disc 20 of any suitable or preferred insulating material, such as a phenol condensation product, or a disc of fibrous material impregnated with the same, is mounted within the ferrule 2 and Seats upon an inner annular shoulder 21 thereof. This ldisc is provided with a central opening 22 which receives a bail 23 formed from a `suitable length of wirewhich possesses sufficient mechanical strength to readily withstand the direct pull of spring 7. The ends of this piece of wire are inserted through opposite openings 24 adjacent the upper end of member 6 and are bent upwardly toproject above this member, after which these ends are twisted together as at 25.

The part between the ends lies at the side of the stem. 6 while the ends are twisted together and after they are twisted together the bail thus formed between the united ends is raised over the top of the stem as shown 'in Fig. 2.- This provides simple and inexpeninvasa@ sive means for producing the bail and attaching it to the terminal member as standard wire of suitable gauge and temper may be employed for this purpose. Thiswire, in addition'to possessing the requisite mechanical strength, should also be a good electrical conductor.

The steni`6 is guided or piloted in the opening 22 of plate 20. The sides of the stem 6 are slabbed oli' at the ends of the openings 24 in said stem to permit the bail 23 to pass through the opening 22 in the plate 20 without binding the same. The upper end of the stem 6 is thereby restrained against any appreciable lateral motion in any direction. This is important in retaining the parts in the desired position, otherwise due to vibration or other causes the parts might be moved into a position where free release and the necessary certainty of operation might be endangered.

Bail 23 engages over a short arm 24 of a main cruciform lever 25 which is fulcrumed at 26 on the upper face of disc 20. The body 27 of this lever is relatively wide and long and spans the opening 22 and the \arm 24 is bent upwardly to provide a curve which receives the upper portion of the bail, the point at which the load from the spring 7 is applied being closely adjacent fulcrum 26 as will be clear from Fig. 5. A. relatively long arm 28 extends from the other side of body 27 of lever 25 in alignment with arm 24. Arm 28 is held depressed by a trigger,-

finger 29 at the upper end of arm 30 of a trigger lever 31. Arm 30 is disposed at right angles to lever. 31 and extends through an upwardly flaring opening 32 through the disc, this arm being fulcrumed at 33 at the edge of opening 32, this ulcrum being therefore, closely adjacent the angle between linger 29 and arm 30 so that the length of the lever arm acting upon arm 28 is very short. A fuse is secured at 35 to arm 36 of lever 31, this arm being of relatively great length. To insure good electrical contact between the fuse and arm 35 the fuse is wrapped about the arm for a considerable portion of its length, as illustrated. The other end portion of this fuse is wrapped about a screw 36 threaded through the supporting disc 20. This wrapped portion of the fuse is clamped'between a washer 37 with which the head of the screw contacts and a strip of tinfoil 38 which extends over the upper face of the disc and is bent downwardly about the edge thereof and under the disc to form a contact element 39 which is held pressed firmly against the upper face of shoulder 21. Electrical and mechanical connections are thus established between the ter- .minal member 6 and ferrule 2, the mechanical connections giving the fuse 34 a great mechanical advantage over the spring 7. This fuse passes through a small opening 34a in the disc 20 and is thus enclosed so as to be protected from mechanical injury.

' Attention is called to the fact that the fuse wire 34 is shunted at each end by a suitable conductor so as to define a portion of least current 'carrying capacity in the opening 34". At its upper end the fuse wire 34 is shunted by the metal plate or foil 38 from the terminal screw 36 to the upper end of hole 34, and at its lower end the said fuse wire is shunted by the lever arm 36 upon which the same is wrapped. As a result the fuse will invariably yield in the vertical portion lying in said hole 34a and offer no hindrance to downward pull of the lever arm 36. This assuresthe necessary certainty of operation.

The fuse 34 is formed from a suitable length of small diameter wire of material possessing the proper electrical conductivity and mechanical strength. For this purpose I preferably use nickel chromium alloy wire, tholgh other suitable materials might be use The fuse structure is installed in a known manner with the ferrule'2 uppermost. The current passes from ferrule 2 through the fuse 34 and the system of levers to terminal 6 and then 'ferrule 3. The fuse is connected in series with the terminal member and is quickly fused or melted when the current exceeds a predetermined maximum.

The fuse here shown is .adapted for use in circuit'with a potential transformer. The current required normally is very small and hence the fuse must operate at a current value which represents an overload for such a piece of apparatus. The particular fuse shown in Figs. 1 to 6 is a 7.5 k. v. fuse rated to blow at a value of 9 amperes. It will be appreciated therefore that the mechanical strength of a conductor adapted to blow at such a small current value is not at all adequate to sustain the ltension of the powerful spring which is desirable to do the work of drawing the movable terminal down into the liquid to quench the arc. This principle may be employed on small capacity fuses for general By employing a connection between the terminal member 6 and the fuse which gives the fuse a mechanical advantage over the spring 7, it is possible to employ a fuse of very ne'wire with the advantages noted. It is also to be noted that this fuse is held under tension by theaction of the lever systemyso that the terminal member 6 is released instantaneously ,upon blowing of the fuse and is drawn away from ferrule 2 by the action of spring 7. the arc being drawn in barrel 1. In .practice this barrel is filled with a suitable arc quenchingliquid, such as carbon tetrachloride. v A portion of this quenching liquid is forced upwardly through the follower 15 during the downward movement thereof in opposition to any arc which may be drawn in the liquid and this, combined with the quenching properties ofthe liquid, serves to very quickly quench the arc.

After the fuse 34 has been blown it can be readily replaced by a new fuse rendering the device ready for further use.

In the modified form illustrated in Figure 7, I provide a separable connection /40 between the ferrule and the movable terminal 6. This connection includes two sections 41 and 42 of electrical insulating material. Section 42 is threaded into the upper end of terminal member 6 and section 41 is held against downward movement by'a rod 43 of electrical conducting material passing through this section diametrically thereof, the end portions of this rod seating upon shoulder 21. The two sections are cut away to provide overlapping portions, as illustrated, these portions being of approximately semi-cylindrical shape with their flat faces in Contact. Each of the overlapping portions of the sections is provided in its innery face with a recess, these recesses being aligned 1 and receiving a cylindrical spreading pin or key 44. The intermediate portion of the connecting structure 40 is spirally threaded or grooved for reception of a fuse 34" wrapped about the same. One terminal of this fuse is wrapped at 44 about rod 43 and soldered or otherwise secured thereto to form .a close electrical connection. The other ter- 'minal of this fuse is soldered or otherwise suitably secured to terminal member 6 at 45.

The wire 34" at its end turns is clamped under the heads of screws 48 to keep it from nnwrapping or loosening as this wire is relatively stiff and springy and tends to spring away from contact with the stem 40. The same construction is employed in Fig.` 8. The fuse 34b serves to normally confine the overlapping portions of sections 41 and 42 laterally and the key 44 serves to lock these sections together so as to hold them against relative axial movement. W'hen the fuse is blown the sections 41 and 42 are released and, due to the tension of spring 7, section 42 is moved downwardly, the cylindrical pin or key 44 acting at this time with a cam action to force the two sections apart completely releasing them and permitting downward movement of terminal member 6 in to its extreme lower position. To facilitate separation of the members of the connections, the wire of fuse 34b is preferably sufficiently resilient to insure that it will quickly free itself from about the connection when the fuse is blown. In this form, as in the form In the modified form illustrated in Fig. 8, the two sections 41a and 42a of the connection 40a are provided with overlapping elements 46 and 47, respectively. These elements are of substantially wedge shape and diverge away from the Vrespective sections, having their inner flat surfaces held in contact by the wrapping of fuse 34".v In this form, the opposite inclination of the contacting surfaces of elements 46 and 47, and the form of these elements, serve to etfectually lock the two sections of the connections against relative axial movement so long as the sections are confined laterally by the fuse. Upon blowing of the fuse the sections are no longer confined laterally and movement of section 42a by spring 7 results in the sections being forced apart laterally so as to effectually vfree lthem from the fuse, destroying the mechanical connection between the fuse and the movable terminal member, permitting this member to be moved downwardly in barrel l at high speed by the action of spring 7. This form also gives the fuse a decided mechanical advantage over the spring.

One or more flexible conductors might be connected across the joints of the leverage system if desired. l

Obviously, instead of a compound lever a single lever might be employed Within my invention.

.What I claim is 1. In a fuse structure of the character described, a ferrule, a terminal member, means urging said member away from the ferrule, and'mechanical connections between the ferrule and t-he terminal member' normally holding said member against movement, the connections including a fusible element and means acting length-wise thereof through said fusible element to restrain releasing of said connections, the fusible element establishing electrical connection between the ferrule and the terminal member.

2. In a fuse structure of the character described, a ferrule, a yterminal member, operating meansurging the terminal member away from the ferrule, a fuse connected between the terminal member and the ferrule, said fuse being ofinsuilicient mechanical strength to sustain the force of said means, and releasable means through which the force is transmitted to the fuse, the releasable means giving said fuse aI mechanical advantage over c said operating means.

3. In a fuse structure of the character described,two terminal members havingrelative movement, operating means acting to separate said members, and releasable means connecting the terminal members mechanically and electrically, said connecting means including a fuse of insuliicient mechanical strength to sustain the force of the operating means, the connecting means also including means through which the force is transmitted to the fuse and giving the fuse a mechanical advantage over the operating means.

4. In a fuse structure of the character described, two terminalmembers lhaving relative movement, o erating means acting to separate said mem rs, releasable means connecting the terminal members mechanically and electrically, said connecting means in cluding a fuse of insufficient mechanical strength to sustain the force of the operating means and maintained under tension thereby, the connecting means also including means giving the fuse a mechanical advantage over the operating means. a,

5. In a fuse structure of the character described, two terminal members having relative movement, operating means acting to separate said members, releasable means connecting the terminal members mechanically and electrically, said connecting means including a fuse in series with the terminalmembers and of insutlicientmechanical strength to sustain the force of the operating means, the connecting means also including means giving the fuse a mechanical advantage over the operating means.

6. In a fuse structure of the character described, a stationary terminal, a movable terminal, operating means urging the movable terminal away from the stationary terminal, a fuse electrically connected to the stationary terminal, releasable lever connections con- 'l necting the fuse and the movable terminal and giving said fuse a mechanical advantage over said operating means, the fuse be-r ing held against movement in the direction of the movable terminall and being electrically connected to the movable terminal by the lever connection.

7. In a fuse structure of the character described, a stat-ionary terminal,a movable terminal, operating means urging the movable terminal away from the stationary terminal, a fuse electrically connected to the stationary terminal, and releasable lever connections connecting thenfuse and the movable terminal and acting to tension the fuse and give it a mechanical advantage over the operating means, t-he fuse being held against movement in the direction of the movable terminal.

8. In a fuse structure of the character described, a ferrule, a supporting member of insulating material mounted in the ferrule and held against movement inwardly thereof, a' terminal member inwardly of said supporting member, operatin means urging the terminal member away rom the ferrule, a fuse establishing electrical connection between the ferrule and the terminal member and held against movement inwardly of the ferrule, and a releasing lever system mounted on the supporting member and forming mechanical connections between the fuse and the op` erating means, said lever system maintaining the fuse element under tension and giving it a mechanical advantage over the operating means.

9. In a fuse str ucture of the character described, a ferrule, a supporting member'of insulating material mounted in the ferrule and held against movement inwardly thereof, a terminal member inwardly of said supporting member, operating means urgingthe terminal member away from the ferrule, a fuse secured to the supporting member and establishing electrical connection between the ferrule and the terminal member and held against movement inwardly of the ferrule, and a releasing lever system mounted on the supporting member and forming mechanical connections between the fuse and the operating means, said lever system maintaining the fuse element under tension and giving it a mechanical advantage over the operating means.

10. In a fuse structure of the character described, a ferrule, a supporting member of insulating material mounted in the ferrule and held against movement inwardly thereof, a terminal member inwardly of said supporting member, operating means urging the termnial member away 4from the ferrule, a fuse establishing electrical connection between the ferruleand the terminal member and held against movement inwardly of the ferrule, and a releasing compound lever system mounted on the supporting member and forming mechanical connections between the fuse'and the operating means, said lever system maintaining the fuse element under tension and giving it a mechanical advantage over the operating means. l

11. In a fuse structure of the character` described, a ferrule, a supporting member of insulating material mounted inthe ferrule and held against movement inwardly thereof, a terminal member inwardly of said supporting member, operating means urging the terminal member away from the errule, a fuse establishing electrical connection between the ferrule and the terminal member and held against movement inwardly of the ferrule,.and a releasable mechanical connection between the fuse and the terminal member, said connection being controlled by the fusefand giving said fuse a mechanical advantage over the operating means.

12. In a fuse structure of the character described, a stationary terminal member, a movable terminal member, operating means urging the movable member away from thev stationary member, a fuse secured at one end and electrically connected to the stationary terminal member, and means securing the other end of the fuse to the movable terminal member, said securing means giving the fuse a mechanical advantage over the operating means, the fuse having electrical connection with the movable terminal member.

13. In a fuse structure of the character described, two terminal members having relative movement, operating means vacting to separate said members, a fuse secured against movement relative to one of the members and electrically connectin both of said members, and means securing the fuse to the other terminal member, said securing means giving the fuse a mechanical advantage over said operating means.

14. In a fuse structure of the character de-V scribed, two terminal members having relative movement, operating means acting to separate saidmembers, a fuse secured against movement relative to one of the members and electrically connecting both of said members, and lever means securing the fuse to the other terminal member, said securing means givin the fuse a mechanical advantage over said operating means.

15. In a fuse structure of the character described, two terminal members having relative movement, operating means acting to separate said members, a fuse secured against movement relative to one of theinembers and electrically connecting both of said members, and a compound lever system securing the fuse to the other terminal member, said lever system giving the'fuse a mechanical advantage over said operating means.

16. In a fuse structure of the character described, a ferrule, a supporting member of insulatingl material mounted in the ferrule and held against movement inwardly thereof a -fuse secured at one end to said member an electrically connected'to the ferrule, a movable terminal member inwardly of the ferrule,

' voperating means urging the terminal member awa from said ferrule, and electricaland mec anicl connections between the fuse and the terminal member, said connections giving the fuse a mechanical advantage over Vthe operating means. l

17. In a fuse structure of the character described, a ferrule, a supportingV member of insulating material mounted in the ferrule and held against movement inwardly thereof, a fuse secured at one end to said member and electrically connected to the ferrule, a movable terminal member inwardly of the ferrule, operating means urging the terminal member away from said ferrule, a main lever mounted on the supporting members, connections between the lever adjacent the ful crum thereof and the terminal member, said connections being released upon movement of the lever out of operative position, and a trigger lever having a finger-engaging over the main lever remote from the fulcrum thereof and holding said main lever in operative position, the trigger lever being ful- 18. In a fuse structure of the character clescribed, an upper ferrule, a supporting member of insulating material mounted in the ferrule and held against downward movement, a terminal member below the `ferrule, means urging said member downwardly, the supporting member having an opening, a main lever fulcrumed on the upper face of said supporting member and having an arm projecting over said opening, a bail secured to the terminal member and engaging over said arm closely adjacent the fulcrum of the lever, a trigger lever on the under face of the supporting member and provided at one end with an upwardly directed arm having a finger at its upper end projected over the main lever remote from the fulcrum thereof, the supporting member having -an opening accommodating the upwardly directed arm and the trigger lever being fulcrumed adjacent said upwardly directed arm, and a fuse secured at one end to the supporting member and electrically connected to the ferrule, the other end of the fuse being secured to the trigger lever remote from the fulcrum thereof.

19. In combination, a pair of terminals,`

means tending to move one of them, a leverage system having a fulcrum relatively rigid with the other terminal, said one terminal being connected to a short arm of said leverage system and a fuse connected between said terminals and holding a long arm of sald leverage system.

20. In a fuse structure, a fusible member, a movable member in series therewith, said movable member being held in position by the fusible member and being released upon the fusing thereof to rapidly increase the gap in the circuit, said fusible member being in non-alignment with the path of movement of the releasable member and being connected therewith by means whereby a small force in the fusible member will counter balance a. great force applied at the movable member.

21. In a fuse structure, a fusible member, a movable member in series therewith, said movable member held in position by the fusible member and being released upon the fusing thereof to rapidly increase the gap in theA circuit, and means for accelerating the movement of the' movable member, said fusible member supporting said movable member through means whereby a small force in thefusible mem-ber' will counterbalance a great force applied at the movable member.

22. In a fuse structure of the character described, two terminal members, operating means urging one of said members away from the other member, a separable connectlonl setwo sections of insulating material secured to the respective terminal members and having associated means normally locking the sections against relative axial movement and acting to force said sections apart laterally upon relative axial movement thereof, and a fuse electrically connecting the terminal members and wrapped about the sections of saidv connection and holding them in operative relation.

24. In a fuse structure of the character described, two terminal members, operating means urging one of said members away from the other member, a separable connection between the terminal members, said connection including two sections of insulating material secured to the respective terminal members and disposed in overlapping relation, a fuse electrically connecting the terminal members vand confining said sections laterally, and

means locking the sections together when they are confined by the fuse, said means forcing the sections apart bv'a camming action when they are released tby the fusing of said fuse. l

25. In a fuse structure of the character described, two` terminal members, operatingl means urging one of said members away from the sections having aligned recesses disposed transversely of their overlapping faces, and a key fitting in said recesses and normally locking the sections of the connections together againstrelative axial movement, the lateral portions of said key being inclined to force the sections'apart upon destruction of the fuse. y

26. In a fuse structure of the character described, two terminal members, operating means urging one of said members away from the other member, said connection including two sections of insulating material secured to the respective terminal members and disposed in overlapping relation, the overlaping portions of said sections diverging away om the respective sections, and a fuse electrically connecting the terminal members and confining the overlapping portions of the connection sections laterally with their inclined faces in contact.

In Witness whereof, l hereunto subscribe my name this 24th day of January, 1927.

NICHOLAS J. CONRAD. 

